This invention relates generally to transfer cases for selectively routing drive torque to different sets of traction wheels of vehicles and more particularly to new and improved compact transfer cases featuring innovative lock-up shift collar and rod arrangements operatively connected to external actuators selectively controlled by the vehicle operator for selective shifting between the sets of traction wheels.
For enhancing mobility and traction of wheeled vehicles, drive torque transfer cases have been employed for shifting drives between various sets of drive wheels, such as between two-wheel drive and four-wheel drive. Those transfer cases frequently comprise a main power shaft for driving a first set of two traction wheels for two-wheel drive and an auxiliary power shaft selectively conditionable for driving a second set of two traction wheels and establishing four-wheel drive. The auxiliary output shaft is commonly driven via a chain belt extending around drive and driven sprockets respectively mounted on the power and auxiliary shafts. To shift from two-wheel to four-wheel drive, a clutch collar is shifted axially from a disengaged position on the main power shaft where the drive sprockets rotate with respect to the main power shaft to an engaged position where the drive sprocket is fixed to and is rotationally driven by the main power shaft. When this occurs, drive torque is split between the full-time drive wheels and the auxiliary drive wheels so that the shift to four-wheel drive is complete. The shift mechanism for the clutch collar typically comprises a shift fork that has a yoke at an inboard end that operatively fits into a groove of the clutch collar and a connector at the outboard end attached to a shift rod so that axial movement of the shift rod can axially move the shift fork and clutch collar. The shift rod and the associated fork may be shifted by the vehicle operator manually through a lever and linkage system or by power assist fluid or electric motor power units. Examples of such systems and units are disclosed in U.S. Pat. No. 2,887,201 granted May 19, 1959 to Delbert Elwood Willis and U.S. Pat. No. 4,381,828 granted May 3, 1983 to Poyston C. Lunn et al.
However, such shift fork, shift rod and rod actuator arrangements are bulky, space-consuming constructions that require large case housings, and are not practical for many current or forthcoming vehicles, particularly those that have crowded or limited space and require small and narrow case housings. New and improved compact transfer cases with advanced traction drive selection constructions meeting higher operating and spatial efficiency standards are accordingly needed for such vehicles.
This invention meets such requirement and standards with the provision of a new and improved compact transfer case, which is mechanically and spatially efficient and suitable for numerous current and advanced vehicle designs. The transfer case of this invention advantageously incorporates advanced transmission components and features and meritoriously combines them with new and improved constructions to provide at least first and second power path operating modes for selecting and delivering torque to the diverse sets of traction wheels of a vehicle. A special main power shaft unit is utilized for the full time drive for a first set of drive wheels while an auxiliary drive is employed for the selective drive of a second set of drive wheels. This auxiliary drive incorporates new and improved shifting components that are encapsulated and telescopically packaged and arranged so that space is more effectively utilized and the casing profile is optimized.
More particularly, the drive selection construction of the transfer case of this invention embraces an advanced telescoping clutching unit comprising a torque-transmitting clutch collar and an associated shifter rod or rod, normally blocked out by new and improved blocker spring construction acting on the rod. This shifter rod construction is axially displaced or actuated by a compact and straightforward drive transfer mechanism for operatively connecting and disconnecting the main and the auxiliary drive shafts with respect to one another. The clutch collar actuator includes a shift rod supported for rectilinear movement in a direction coaxial to the longitudinal axis of one of the drive shafts in response to an axial input force for selection of the various traction drives of the transfer case. Preferably, the shift rod is supported for limited telescoping movement with respect to the auxiliary drive shaft. The auxiliary drive shaft is supported by and is adapted to be drivingly connected to a rotary output sprocket or drive transfer output member by the rotatable torque-transmitting clutch collar operatively mounted internally in these components.
The shift rod preferably extends axially through a bore of the output sprocket and telescopes in an aligned bore of the auxiliary drive shaft to enhance the compactness of this space saver construction. The rotatable clutch collar is carried on the shift rod and axially slides within the aligned bore of the auxiliary drive shaft when the rod is axially shifted. The shift rod has an outboard end extending from the housing of the case into operative communication with external shift actuator construction operable to apply an axial force to the shift rod to effect clutch collar shifting and traction selection. Splined sections of the clutch collar and the output sprocket are selectively interconnected to effect the traction drive to a second set of drive wheels. This invention can be readily extended to provide a two speed in the main power shaft of the transfer case, an additional drive for power take-off, and multiple clutching units providing a package which can be effectively utilized for vehicle towing.